Support design for the diversion tunnel of Diamer Basha Dam, Pakistan,considering the recent developments in empirical systems

Abstract

The use of rock mass rating (RMR) and tunneling quality index (Q) systems in drill and blast tunneling for support design is necessary in the current practice worldwide as these systems are developed empirically for this particular purpose. However, due to the modifications of individual system, no comparison has been made between their suggested support in tunnel design. Empirical rock mass classification systems are continuously updated to reach a reliable support system for construction of tunnels in rocks. This paper presents the utilization of updated versions of RMR and Q system in empirical support design of a diversion tunnel located at Diamer Basha dam site, Pakistan. The rock mass along the alignment of tunnel is divided into different geological units based on rock mass quality, assessed from borehole data. From comparison of recommended support system by RMR and Q system, it is concluded that the RMR system recommend heavy support as compared to Q system. A linear correlation is also obtained between RMR and Q system for the same rock mass which shows a comparatively better correlation coefficient.